dm-mpath: do not activate failed paths

activate_path() is run without a lock, so the path might be
set to failed before activate_path() had a chance to run.
This patch add a check for ->active in activate_path() to
avoid unnecessary overhead by calling functions which are known
to be failing.
Signed-off-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-mpath.c

@@ -1195,8 +1195,11 @@ static void activate_path(struct work_struct *work)
 	struct pgpath *pgpath =
 		container_of(work, struct pgpath, activate_path.work);
 
+	if (pgpath->is_active)
 		scsi_dh_activate(bdev_get_queue(pgpath->path.dev->bdev),
 				 pg_init_done, pgpath);
+	else
+		pg_init_done(pgpath, SCSI_DH_DEV_OFFLINED);
 }
 
 static int noretry_error(int error)